Piezoactuator and drive circuit therefor

ABSTRACT

A piezoactuator has a diaphragm, and the diaphragm has flat piezoelectric elements that oscillate in a longitudinal oscillation mode and a sinusoidal oscillation mode. A first electrode for detecting oscillation in the longitudinal oscillation mode, and a second electrode for detecting the amplitude of oscillation in the sinusoidal oscillation mode, are disposed on the surface of the diaphragm. When the piezoactuator is driven with a drive signal, the phase difference of a first detection signal output from the first electrode and a second detection signal output from the second electrode is detected. The frequency at which the detected phase difference becomes the maximum phase difference is then obtained, and a drive signal of a matching frequency is applied to the piezoelectric elements.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a piezoelectric actuator having apiezoelectric device and to a drive circuit for the same.

RELATED ART

Piezoelectric devices feature outstanding response and efficiencyconverting electrical energy to mechanical energy. As a result, varioustypes of piezoelectric actuators that use the piezoelectric effect ofpiezoelectric devices have been developed in recent years. Thesepiezoactuators are used in such fields as piezoelectric buzzers, inkjetheads for printers, and ultrasonic motors. Using piezoactuators in thecalendar display mechanism in wristwatches and other such applicationswhere there is strong demand for size reductions has also beeninvestigated in recent years.

Wristwatch calendar display mechanisms to now are generally configuredto drive the date counter by indirectly transferring rotational drivepower from an electromagnetic stepping motor to the date counter andsuch through the wheel train of the movement. Wristwatches are worn heldto the wrist with a band and for the convenience of such portability arepreferably thin. It is therefore necessary to also make the calendardisplay mechanism thin.

A thin calendar display mechanism is also desirable from the perspectiveof improving watch production efficiency. First, there are watches witha calendar display mechanism provided in the watch, and there arewatches that are not equipped with a calendar display mechanism. Overallwatch production efficiency can be improved if a common mechanicalsystem for advancing the hands (the “movement”) can be used in bothwatch types. This is because a production system whereby, for example,the movements are mass produced for both watch types and then assembledto the two types of watches, and the calendar display mechanism is thenassembled to only the one type of watch, can be used. In order to usesuch a production system, however, it is necessary to be able to placethe calendar display mechanism on top of the movement, that is, on theface side. In order to do this, it is necessary to configure thecalendar display mechanism so that it is thin enough to fit on the faceside.

While there has thus been a strong desire for thinning the calendardisplay mechanism, the stepping motors used in the calendar displaymechanism are configured such that the coil and rotor and such parts aredisposed perpendicularly to the display face, and there is a limit tohow thin these can be made. Conventional calendar display mechanismsusing a stepping motor are thus not suited to wristwatches that must bemade thin.

It is also particularly difficult when using an electromagnetic steppingmotor as the power source to make a calendar display mechanism thinenough to be placed on the face side. It has therefore been necessary toseparately design and manufacture the movements depending upon whether acalendar display mechanism is included or not when watches with acalendar display mechanism and watches without a calendar displaymechanism are both manufactured.

Considering this background an actuator other than a stepping motorsuitable for configuring a thin calendar display mechanism has beendesired. This has led to the above-noted piezoactuators being studiedfor use as such an actuator.

There are, however, problems related to using a piezoactuator in thecalendar display mechanism of a watch.

First, displacement of the piezoelectric device is dependent upon thevoltage of the supplied drive signal but is very low and normally on thesubmicron order. Displacement produced by the piezoelectric device istherefore amplified by some amplifying mechanism and transferred to thedriven part. However, energy to drive the amplifying mechanism is alsoconsumed when an amplifying mechanism is used, thus leading to a problemof lower efficiency. A further problem is that when an amplifyingmechanism is used the size of the device becomes larger. A yet furtherproblem is that when an amplifying mechanism is interposed it isdifficult to stably transfer drive power to the driven part.

Small portable devices such as wristwatches are battery driven and it istherefore necessary to minimize power consumption and drive signalvoltage. When assembling a piezoactuator into such portable devices apiezoactuator with high energy efficiency and low drive signal voltageis therefore required.

A piezoactuator having a diaphragm made from a thin rectangularpiezoelectric device to which a drive signal is applied to make thepiezoelectric device expand and contract lengthwise and excitelongitudinal oscillations, and mechanically inducing sinusoidaloscillations by means of the longitudinal oscillations, has beenproposed as a high efficiency actuator that can be included in compactdevices.

By producing both longitudinal oscillations and sinusoidal oscillationsin the diaphragm, this type of piezoactuator moves the part of thepiezoactuator in contact with the driven part in an elliptical path.While being small and thin, this piezoactuator can drive with highefficiency.

While it is relatively easy to control the longitudinal oscillationsproduced by the piezoelectric device with this piezoactuator bycontrolling the voltage of the drive signal, easily and accuratelycontrolling the sinusoidal oscillations induced according to themechanical characteristics of the diaphragm is difficult. It hastherefore been difficult to drive this type of piezoactuator withstability and high efficiency.

SUMMARY OF THE INVENTION

An object of this invention is to provide a drive circuit capable ofstably and highly efficiently driving a piezoactuator.

To achieve this object, the present invention provides a drive circuitfor a piezoactuator of which a major component is a diaphragm that is adiaphragm made from piezoelectric elements and oscillates when an acsignal is applied in a first oscillation mode and a second oscillationmode having a different oscillation direction, the piezoactuator drivecircuit characterized by comprising a driver for applying a drivevoltage signal that is an ac signal to the diaphragm; and a frequencycontrol unit for detecting an electrical signal from the diaphragmrepresenting oscillation in the first oscillation mode and an electricalsignal representing oscillation in the second oscillation mode, andapplying frequency control of the drive voltage signal to optimize thephase difference between these signals. This is a first embodiment(basic embodiment) of a piezoactuator drive circuit provided by thepresent invention.

By thus optimally controlling the phase difference, driving thepiezoactuator at consistently high efficiency is enabled by the presentinvention.

In a preferred embodiment the frequency control unit is a circuit forfrequency controlling the drive voltage signal so that the phasedifference is substantially maximized. This is a second embodiment of apiezoactuator drive circuit provided by the present invention.

The frequency control unit in this case preferably has a phasedifference detection circuit for detecting, for example, a phasedifference between an electrical signal representing oscillation in thefirst oscillation mode and an electrical signal representing oscillationin the second oscillation mode; a circuit for determining a timederivative of the phase difference detected by the phase differencedetection circuit; and a circuit for increasing the drive voltage signalfrequency when the time derivative is positive, and decreasing the drivevoltage signal frequency when negative. This is a third embodiment of apiezoactuator drive circuit provided by the present invention.

In a preferred embodiment the drive circuit further has avoltage-controlled oscillator for supplying an output signal to thedriver; and the frequency control unit controls the frequency of thedrive voltage signal by increasing or decreasing the frequency controlvoltage applied to the voltage-controlled oscillator. This is a fourthembodiment of a piezoactuator drive circuit provided by the presentinvention.

In a further preferred embodiment the frequency control unit comprisesmemory and means for storing to the memory the voltage level of thefrequency control voltage when the frequency of the drive voltage signalis controlled to maximize the phase difference; and the frequencycontrol unit determines the initial frequency control voltage based onthe voltage level stored to memory when starting drive voltage signalfrequency control by increasing or decreasing the frequency controlvoltage. This is a fifth embodiment of a piezoactuator drive circuitprovided by the present invention.

In another preferred embodiment the frequency control unit applies drivevoltage signal frequency control so that the phase difference goes to areference phase difference. This is a sixth embodiment of apiezoactuator drive circuit provided by the present invention.

The frequency control unit in this case comprises a phase differencedetection circuit for detecting, for example, a phase difference betweenan electrical signal representing oscillation in the first oscillationmode and an electrical signal representing oscillation in the secondoscillation mode; a comparison circuit for comparing the phasedifference detected by the phase difference detection circuit and thereference phase difference; and a frequency adjusting circuit forincreasing or decreasing the drive voltage signal frequency according tothe comparison result of the comparison circuit. This is a seventhembodiment of a piezoactuator drive circuit provided by the presentinvention.

In a preferred embodiment the frequency control unit further comprises avoltage-controlled oscillator for supplying an output signal to thedriver; and the frequency adjusting circuit is comprised of a voltageadjusting circuit for increasing or decreasing the frequency controlvoltage applied to the voltage-controlled oscillator based on thecomparison result of the comparison circuit. This is an eighthembodiment of a piezoactuator drive circuit provided by the presentinvention.

Furthermore, in a preferred embodiment the frequency control unitcomprises a drive pass/fail evaluation means for determining ifpiezoactuator drive succeeded or failed; and an initial reference phasedifference adjusting means for reducing the reference phase differenceuntil successful when piezoactuator drive fails, and increasing thereference phase difference when successful. This is a ninth embodimentof a piezoactuator drive circuit provided by the present invention.

The initial reference phase difference adjusting means may omit for aspecified period the process for increasing the reference phasedifference when the reference phase difference at which piezoactuatordrive succeeds is the same for a specific consecutive number of times.This is a tenth embodiment of a piezoactuator drive circuit provided bythe present invention.

In a preferred embodiment the frequency control unit has a frequencycounter for measuring the frequency of the drive voltage signal; and thedrive pass/fail evaluation means determines if piezoactuator drivesucceeded or failed based on whether the frequency measurement of thefrequency counter is within an appropriate range or not. This is aneleventh embodiment of a piezoactuator drive circuit provided by thepresent invention.

In a preferred embodiment the frequency control unit comprises means forobtaining, each time the piezoactuator is driven, change from a previousdrive operation in the phase difference between an electrical signalfrom the diaphragm representing oscillation in the first oscillationmode and an electrical signal representing oscillation in the secondoscillation mode; and means for increasing or decreasing the referencephase difference according to change in the phase difference. This is atwelfth embodiment of a piezoactuator drive circuit provided by thepresent invention.

This invention also provides in a control method for a drive circuithaving a driver for applying a drive voltage signal that is an ac signalto a diaphragm of a piezoactuator, a voltage-controlled oscillator foroutputting a drive voltage signal of a frequency corresponding to afrequency control voltage to the driver, and a phase differencedetection circuit for receiving an electrical signal from the diaphragmrepresenting oscillation in a first oscillation mode and an electricalsignal representing oscillation in a second oscillation mode with anoscillation direction different from the first oscillation mode, anddetecting a phase difference of these electrical signals, apiezoactuator drive circuit control method characterized by comprising:a frequency control step for optimizing the oscillation frequency of thevoltage-controlled oscillator based on the phase difference detected bythe phase difference detection circuit.

In a preferred embodiment the frequency control step has a step forincreasing the oscillation frequency of the voltage-controlledoscillator if the time derivative of the phase difference detected bythe phase difference detection circuit is positive, and decreasing ifnegative, until change in the phase difference over time is within aspecific range.

In a separate preferred embodiment the frequency control step has a stepfor increasing the oscillation frequency of the voltage-controlledoscillator until the phase difference is greater than or equal to areference phase difference.

In this embodiment a step for determining if driving the piezoactuatorsucceeded or failed, and correcting the reference phase difference basedon the result, may also be provided.

In addition to modes in which products comprising the above-describeddrive circuit are manufactured or sold, the present invention can alsobe achieved by modes such as distributing a program for executing theabove-described methods to users via an electrical communicationcircuit, or distributing a computer-readable storage medium storing sucha program to users.

From yet a further perspective, this invention provides a piezoactuatorcharacterized by comprising: a diaphragm of which piezoelectric elementsare major components for oscillating when an ac signal is applied in afirst oscillation mode and a second oscillation mode having a differentoscillation direction; a first oscillation detection electrode disposedon a surface of the diaphragm to detect oscillation in the firstoscillation mode; and a second oscillation detection electrode disposedon a surface of the diaphragm to detect oscillation in the secondoscillation mode.

In a preferred embodiment the first oscillation mode is a longitudinaloscillation mode, and the second oscillation mode is a sinusoidaloscillation mode.

In a preferred embodiment the piezoactuator has a contact part that is amember for contacting the rotor of a drive mechanism, moving in anelliptical path described by oscillation in the longitudinal oscillationmode and oscillation in the sinusoidal oscillation mode produced in thediaphragm, and rotationally driving the rotor.

From yet another perspective, the present invention provides a portableelectronic device characterized by comprising a piezoactuator and adrive circuit, the piezoactuator having as a major component a diaphragmmade from piezoelectric elements and oscillating when an ac signal isapplied in a first oscillation mode and oscillating in a secondoscillation mode having a different oscillation direction; and the drivecircuit having a driver for applying a drive voltage signal that is anac signal to the diaphragm, and a frequency control unit for detectingan electrical signal from the diaphragm representing oscillation in thefirst oscillation mode and an electrical signal representing oscillationin the second oscillation mode, and applying frequency control of thedrive voltage signal to optimize the phase difference between thesesignals.

This portable electronic device uses any one of the above-describedtwelve embodiments as the drive circuit, but can use the second totwelfth embodiments.

In a preferred embodiment the portable electronic device is a wristwatchcomprising a rotor rotationally driven by the piezoactuator; and adisplay mechanism linked to the rotor for displaying information relatedto time.

In a separate preferred embodiment the portable electronic device is acontactless IC card.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing the configuration of the major parts of awristwatch calendar display mechanism having assembled therein apiezoactuator according to a first embodiment of this invention.

FIG. 2 is a section view showing the basic configuration of the samewristwatch.

FIG. 3 is a section view showing the basic configuration of the samecalendar display mechanism.

FIG. 4 is a plan view showing the detailed configuration of the samepiezoactuator.

FIG. 5 is a section view showing the configuration of the diaphragm ofthe same piezoactuator.

FIG. 6 shows an example of electrodes formed on the surface of thepiezoelectric device in the same piezoactuator.

FIG. 7 and FIG. 8 show polarization states of the same piezoelectricdevice.

FIG. 9 shows sinusoidal oscillation produced in the diaphragm.

FIG. 10 shows the elliptical motion produced in the end contact part ofthe diaphragm.

FIG. 11 to FIG. 14 show change to the drive frequency of detectionsignals obtained from the oscillation detection electrodes of thediaphragm.

FIG. 15 and FIG. 16 show sample arrangements of the oscillationdetection electrodes of the diaphragm.

FIG. 17 is a block diagram showing the configuration of a drive circuitfor a piezoactuator according to a first embodiment of this invention.

FIG. 18 shows examples of change in the path of the contact part in thepresent embodiment due to the drive frequency.

FIG. 19 shows examples of change in the rotational speed of the rotorand change in the phase difference of the longitudinal oscillation andsinusoidal oscillation detection signals in the same embodiment when thefrequency of the drive voltage signal applied to the diaphragm varies.

FIG. 20 is a block diagram showing the configuration of the φ-Vconversion circuit in FIG. 17.

FIG. 21 and FIG. 22 show the waveform at each part of the same φ-Vconversion circuit.

FIG. 23 is a flow chart showing the operation of the same drive circuit.

FIG. 24 is a block diagram showing the configuration of the drivecircuit in a second embodiment of this invention.

FIG. 25 is a flow chart showing the operation of the same drive circuit.

FIG. 26 and FIG. 27 show the change due to ambient temperature inpiezoactuator characteristics.

FIG. 28 is a block diagram showing the configuration of a drive circuitin a third embodiment of this invention.

FIG. 29 shows an example of the operation of the same drive circuit.

FIG. 30 is a block diagram showing the configuration of a drive circuitaccording to a fourth embodiment of this invention.

FIG. 31 is a flow chart showing the operation of the same drive circuit.

FIG. 32 and FIG. 33 show examples of the operation of the same drivecircuit.

FIG. 34 shows the appearance of a contactless IC card.

FIG. 35 shows the configuration of the remaining balance display counterof the same card.

FIG. 36 is a side view showing the configuration of the high digitdisplay part of the same card.

FIG. 37 is a front view showing the configuration of the low digitdisplay part of the same card.

FIG. 38 is a side view showing the configuration of the low digitdisplay part of the same card.

FIG. 39 and FIG. 40 are block diagrams showing alternative drive circuitconfigurations.

BEST MODE FOR ACHIEVING THE INVENTION

Preferred embodiments of the present invention are described below withreference to the accompanying figures.

[1] Embodiment 1

[1.1] Overall Configuration

FIG. 1 is a plan view showing the configuration of a wristwatch calendardisplay mechanism in which a piezoactuator A according to a firstembodiment of this invention is assembled.

As shown in FIG. 1, the main part of the calendar display mechanism issubstantially configured with a piezoactuator A according to the presentembodiment, rotor 100 rotationally driven by this piezoactuator A, aspeed-reducing wheel train for speed reducing and transferring rotationof the rotor 100, and a date counter 50 rotated by drive forcetransferred through the speed-reducing wheel train. The speed-reducingwheel train includes a date-turning middle wheel 40 and date-turningwheel 60. The piezoactuator A has a flat rectangular diaphragm 10; thisdiaphragm 10 is disposed with the end thereof in contact with theoutside surface of the rotor 100.

FIG. 2 is a section view of the watch shown in FIG. 1. The calendardisplay mechanism comprising the piezoactuator A is assembled at thehatched part in the figure. A disc-shaped dial 70 is disposed above thiscalendar display mechanism. A window 71 for displaying the date isdisposed at one part at the outside of the dial 70 so that the date onthe date counter 50 can be seen through the window 71. The movement anddrive circuit (not shown in the figure) for driving the hands 72 isdisposed below the dial 70.

FIG. 3 is a section view showing the detailed configuration of thecalendar display mechanism shown in FIG. 1. As shown in FIG. 3 the watchhas a base plate 103 that is a first bottom plate, and a second bottomplate 103′ on a different level than the base plate 103. A shaft 101axially supporting the rotor 100 of the calendar display mechanismprojects from the base plate 103. The rotor 100 has a bearing (not shownin the figure) on its bottom, and the end of the shaft 101 is held inthe bearing. A gear 100c that is coaxial to the rotor 100 and turns inconjunction with the rotor 100 is disposed at the top of the rotor 100.

A shaft 41 for axially supporting the date-turning middle wheel 40projects from the base plate 103′. A bearing (not shown in the figure)is disposed to the bottom of the date-turning middle wheel 40, and theend of the shaft 41 is held in the bearing. The date-turning middlewheel 40 has a large diameter part 4b and a small diameter part 4a. Thesmall diameter part 4a is cylindrical with a slightly smaller diameterthan the large diameter part 4b, and has a substantially square notch 4cformed in its outside surface. This small diameter part 4a is affixed tothe large diameter part 4b so that they are concentric. The top gear100c of the rotor 100 meshes with the large diameter part 4b. Therefore,the date-turning middle wheel 40 having large diameter part 4b and smalldiameter part 4a rotates in conjunction with rotation of the rotor 100on shaft 41 as the axis of rotation.

The date counter 50 is ring shaped as shown in FIG. 1, and has internalgear 5a formed on the inside circumference surface. The date-turningwheel 60 has a five tooth gear and meshes with internal gear 5a. Asshown in FIG. 3, a shaft 61 is disposed in the center of thedate-turning wheel 60, and is fit with play in a through-hole 62 formedin the base plate 103′. The through-hole 62 is formed oblongly in thecircumferential direction of the date counter 50.

One end of leaf spring 63 is fixed to base plate 103′ and the other endflexibly presses up and to the right as seen in FIG. 1 on shaft 61. Leafspring 63 urges shaft 61 and date-turning wheel 60. The urging action ofthis leaf spring 63 also prevents rocking of date counter 50.

One end of leaf spring 64 is screw fixed to the second bottom plate103′, and an end part 64a bent substantially in a V-shape is formed onthe other end. Contact 65 is placed so as to contact leaf spring 64 whendate-turning middle wheel 40 turns and end part 64a enters notch 4c. Aspecific voltage is applied to the leaf spring 64, and when it contactscontact 65 the voltage is also applied to the contact 65. It istherefore possible to detect the date counting status by detecting thevoltage of contact 65. It should be noted that a manual drive gearengaging internal gear 5a is also preferably provided so that the datecounter 50 can be driven when a user performs a specific action with thecrown (not shown in the figure).

When a drive voltage is applied from a drive circuit in theconfiguration described above, the diaphragm 10 of the piezoactuator Aoscillates within the plane thereof including the surfaces. The outsidesurface of the rotor 100 is struck by the oscillations produced in thisdiaphragm 10, and the rotor 100 is rotationally driven clockwise asindicated by the arrow in the figure. This rotation of the rotor 100 istransferred through date-turning middle wheel 40 to the date-turningwheel 60, and this date-turning wheel 60 turns the date counter 50clockwise.

It will be noted here that power transfer from the diaphragm 10 to therotor 100, from the rotor 100 to the speed-reducing wheel train, andfrom the speed-reducing wheel train to the date counter 50 is in eachcase the transfer of power in the direction parallel to the surfaces ofthe diaphragm 10. It is therefore possible to dispose the diaphragm 10and rotor 100 in the same plane, rather than stacking a coil and rotorin the thickness direction as with a stepping motor according to therelated art, and the calendar display mechanism can therefore be madethinner. Furthermore, by making the calendar display mechanism thin itis also possible to reduce the thickness D of the hatched part and makethe overall watch thinner.

Furthermore, because it is possible with the present invention to housethe calendar display mechanism in the hatched area in FIG. 2, a commonmovement 73 can be used in watches that have a calendar displaymechanism and watches that do not have a calendar display mechanism, andproductivity can be increased.

Various wristwatches with an electrical generator function have beenproposed recently, and reducing overall watch size has been difficultwith this type of wristwatch because two large mechanical elements mustbe provided, the generating mechanism and a motor mechanism for themovement. However, by using a piezoactuator A according to the presentembodiment of the invention in place of a motor, a thin movement can beprovided and overall watch size can be reduced.

[1.2] Details of the Piezoactuator According to the Embodiment

FIG. 4 is a plan view showing the detailed configuration of thepiezoactuator A. FIG. 5 is a section view through I-I′ of the diaphragm10 in the piezoactuator A. As shown in FIG. 4 the diaphragm 10 is arectangular plate enclosed by two long sides and two short sides. Asshown in FIG. 5, the diaphragm 10 has a lamellar structure with tworectangular flat piezoelectric elements 30 and 31 and disposedtherebetween a stainless steel reinforcing plate 32 of substantially thesame shape as the piezoelectric elements 30 and 31 and thinner than thepiezoelectric elements 30 and 31.

By thus disposing a reinforcing plate 32 between piezoelectric elements30 and 31 damage to the diaphragm 10 caused by excessive amplitude inthe diaphragm 10 or external shock from dropping, for example, isreduced and durability can be improved. Furthermore, by using a partthinner than the piezoelectric elements 30 and 31 for the reinforcingplate 32, interference with oscillation of the piezoelectric elements 30and 31 can be significantly avoided.

The piezoelectric elements 30 and 31 can be made from materials such aslead zirconate titanate (PZT (TM)), quartz, lithium niobate, bariumtitanate, lead titanate, lead metaniobate, polyvinylidene fluoride, zinclead niobate, and scandium lead niobate. The chemical formula for zinclead niobate is [Pb(Zn1/3-Nb2/3)3)1—X (PbTiO3)X] (where X differsaccording to the composition, and X=0.09 approximately), and thechemical formula for scandium lead niobate is [{Pb((Sc1/2-Nb1/2)1—X TiXO3] (where X differs according to the composition, and X=0.09approximately).

As shown in FIG. 4, the diaphragm 10 has a contact 36 at one cornerwhere a long side and a short side intersect. This contact 36 isachieved by cutting or otherwise shaping the reinforcing plate 32 shownin FIG. 5, causing an end part with a gradually rounded surface toproject from the piezoelectric elements 30 and 31. The diaphragm 10 ispositioned with the tip of this contact 36 contacting the outsidesurface of the rotor 100 and the long sides thereof held at an angle ofapproximately 135 degrees to the radius of the rotor 100. A supportmember 11 and spring 300 are disposed to the piezoactuator A in order tohold the diaphragm 10 in this position.

In a preferred embodiment the support member 11 is formed integrally tothe reinforcing plate 32 by cutting or otherwise shaping the reinforcingplate 32. As shown in the figure this support member 11 is an L-shapedmember having a perpendicular part projecting perpendicularly fromsubstantially the center of the long side of the diaphragm 10, and ahorizontal part projecting from the end of this perpendicular partparallel to the long side toward the rotor 100. A pin 39 protruding fromthe base plate 103 as shown in FIG. 1 and FIG. 3 passes through end 38on the opposite end of the horizontal part from the perpendicular part.The support member 11 and diaphragm 10 fixed thereto can turn on thispin 39 as the axis of rotation.

End 300a of spring 300 is engaged with approximately the center part 11aof the horizontal part of the support member 11. A pin 300b protrudingfrom the base plate 103 (see FIG. 1 and FIG. 3) passes throughsubstantially the center of the spring 300. The spring 300 can rotate onthis pin 300b as the axis of rotation. The other end part 300c of thespring 300 on the end opposite end 300a engages the base plate 103. Thepressure with which the contact 36 pushes against the outside surface ofthe rotor 100 can be adjusted in this embodiment by changing theposition of this end 300c.

More specifically, if end 300c is displaced clockwise as seen in thefigure around pin 300b, the force with which end 300a of spring 300pushes up on part 11a of support member 11 increases, and this forcedecreases if end 300c is displaced counterclockwise. If the forcepushing up on the support member 11 increases, the force causing thesupport member 11 to rotate counterclockwise about pin 39 increases, andthe force whereby the contact 36 pushes the rotor 100 increases. On theother hand, if the force pushing the support member 11 up decreases, theforce causing support member 11 to rotate clockwise decreases, and theforce of contact 36 against the rotor 100 decreases. The drivecharacteristics of the piezoactuator A can thus be adjusted by thepressure applied by contact 36 against rotor 100.

It will be noted that in this embodiment the contact 36 pushing againstthe outside surface of the rotor 100 is curved. As a result, contactbetween the outside surface of the rotor 100, which is a curved surface,and the curved contact 36 will not change appreciably even if therelative positions of the rotor 100 and diaphragm 10 vary due todimensional variations, for example. It is therefore possible tomaintain stable contact between the rotor 100 and contact 36.Furthermore, grinding or polishing only needs to be applied to thecontact 36 that contacts the rotor 100 in this embodiment, and managingthe contact with the rotor 100 is therefore simple. A conductor ornon-conductor can be used for the contact 36, but shorting of thepiezoelectric elements 30 and 31 can be prevented when there is contactwith the rotor 100, which is generally made of metal, if a non-conductoris used.

[1.3] Configuration of the Drive Circuit and Electrodes Disposed on theDiaphragm

The drive electrode and oscillation detection electrodes disposed to thediaphragm 10 are described next with reference to FIG. 6. In the exampleshown in FIG. 6 rectangular oscillation detection electrodes T1, T2, T3,and T4 are positioned at the four corners on the surface of therectangular piezoelectric element 30. Although not shown in FIG. 6,oscillation detection electrodes T1, T2, T3, and T4 identical to theseare also located on the opposite side at the corners of piezoelectricelement 31. Oscillation detection electrode T1 located on piezoelectricelement 30 and oscillation detection electrode T1 located onpiezoelectric element 31 are connected, and detection signal SD1representing oscillation of the diaphragm 10 is obtained from a contacttherebetween. Oscillation detection electrode T2 located onpiezoelectric element 30 and oscillation detection electrode T2 locatedon piezoelectric element 31 are likewise connected, and detection signalSD2 representing oscillation of the diaphragm 10 is obtained from acontact therebetween. The other oscillation detection electrodes T3 andT4 are the same. Drive electrode 33 is disposed on the surface ofpiezoelectric element 30 in the area not covered by oscillationdetection electrodes T1 to T4. There is a gap between the driveelectrode 33 and oscillation detection electrodes T1 to T4, which arethus electrically isolated. An identical drive electrode 33 is alsodisposed to the surface of piezoelectric element 31.

Piezoelectric elements 30 and 31 are each polarized in the thicknessdirection. FIG. 7 and FIG. 8 each show examples of the polarizationstates of piezoelectric elements 30 and 31. In this embodiment of theinvention piezoelectric elements 30 and 31 have the property ofexpanding in the longitudinal direction when a field in the samedirection as each direction of polarization is received and contractingwhen a field in the direction opposite the polarization direction isreceived. Therefore, when the arrangement of the polarization directionsof the two piezoelectric elements 30 and 31 is different as shown inFIG. 7 and FIG. 8, the method of driving each piezoelectric element isalso different.

In the example shown in FIG. 7 piezoelectric elements 30 and 31 arepolarized in mutually opposite directions. In this case, as shown inFIG. 6, the reinforcing plate 32 is to ground, the drive electrode 33 onpiezoelectric element 30 and the drive electrode 33 on piezoelectricelement 31 are connected, and a drive voltage signal SDR of a specificfrequency alternating between a +V voltage and −V voltage is repeatedlyapplied between this contact and the ground line. When a +V voltage isapplied between the ground line and the contact between the two driveelectrodes 33, a field opposite each polarization direction is appliedto piezoelectric elements 30 and 31, and piezoelectric elements 30 and31 therefore contract longitudinally. On the other hand, when a −Vvoltage is applied between the ground line and the contact between thetwo drive electrodes 33, a field in the same direction as eachpolarization direction is applied to piezoelectric elements 30 and 31,and piezoelectric elements 30 and 31 therefore expand longitudinally.Because of this behavior the diaphragm 10 expands and contracts in thelongitudinal direction as a result of applying a drive voltage signalSDR of a specific frequency. This expansion and contraction movement iscalled longitudinal oscillation or oscillation in a first oscillationmode.

In the example shown in FIG. 8 the piezoelectric elements 30 and 31 arepolarized in the same direction. In this case the reinforcing plate 32is to ground and a first phase, in which a +V voltage is applied betweenthe ground line and drive electrode 33 on piezoelectric element 30 and a−V voltage is applied between the ground line and drive electrode 33 onpiezoelectric element 31, and a second phase, in which a −V voltage isapplied between the ground line and drive electrode 33 of piezoelectricelement 30 and a +V voltage is applied between the ground line and driveelectrode 33 on piezoelectric element 31, are repeated at a specificfrequency. In this first phase the piezoelectric elements 30 and 31contract longitudinally because a field in the direction opposite eachpolarization direction is applied to piezoelectric elements 30 and 31.In the second phase, on the other hand, the piezoelectric elements 30and 31 expand longitudinally because a field of the same direction aseach polarization direction is applied to piezoelectric elements 30 and31. Longitudinal oscillation is thus produced in the diaphragm 10 byapplying such drive voltages of a specific frequency.

It should be noted that the diaphragm 10 can be made substantiallylinearly symmetrical about an axis of symmetry passing through thecenter in the longitudinal direction, but is not completely symmetricalbecause of such asymmetrical components contained therein as contact 36.As a result, when longitudinal oscillation is produced in the diaphragm10, a moment swinging in the direction perpendicular to the longitudinaldirection of the diaphragm 10 occurs at a delay to this longitudinaloscillation. This moment produces sinusoidal oscillation in thediaphragm 10. As shown in FIG. 9. This sinusoidal oscillation ismovement in which the diaphragm 10 moves in the plane including thesurfaces of the diaphragm 10 perpendicularly to the longitudinaldirection. When such longitudinal oscillation and sinusoidal oscillationis produced in the diaphragm 10, the contact 36 at the end of diaphragm10 moves in an elliptical pattern as shown in FIG. 10. The rotor 100 isthus struck on the outside surface by contact 36 moving in thiselliptical path, and is thus rotationally driven.

The amplitude of the longitudinal oscillation and the amplitude of thesinusoidal oscillation differs according to the position on the surfaceof the diaphragm 10. That is, a phenomenon occurs in which longitudinaloscillation is conspicuous at certain positions on the surface andsinusoidal oscillation is conspicuous at other positions. The diaphragm10 also has a resonance characteristic to the longitudinal oscillationand a resonance characteristic to the sinusoidal oscillation. Resonancewith respect to longitudinal oscillation of the diaphragm 10 andresonance with respect to sinusoidal oscillation is determined by theshape and material of the diaphragm 10, but the latter resonancefrequency is slightly higher than the former resonance frequency.

In this preferred embodiment oscillation detection electrode pairs aredisposed at plural locations on the piezoelectric elements 30 and 31 ofdiaphragm 10, and longitudinal oscillation and sinusoidal oscillationare thereby detected. FIG. 11 to FIG. 14 show the voltage amplitude ofthe detection signals from each of the oscillation detection electrodesT1 to T4 when the frequency of the drive voltage signal SDR applied todrive electrode 33 is changed when a load is not connected to thediaphragm 10.

Referring to FIG. 6, oscillation detection electrodes T1 and T3 aredisposed to positions where longitudinal oscillation of the diaphragm 10is conspicuous. As a result, as shown in FIG. 11 and FIG. 13, theamplitude voltage of the detection signals obtained from theseelectrodes is greatest near the resonance frequency band fr(approximately 283.5 [kHz]) related to longitudinal oscillation of thediaphragm 10. On the other hand, oscillation detection electrodes T2 andT4 are disposed to positions where sinusoidal oscillation of thediaphragm 10 is conspicuous. As a result, as shown in FIG. 12 and FIG.14, the amplitude voltage of the detection signals obtained from theseelectrodes is greatest near the resonance frequency band fr2(approximately 287.5 [kHz]) related to sinusoidal oscillation of thediaphragm 10. This tendency is the same when a load is connected to thediaphragm 10.

Various methods of arranging the oscillation detection electrodes otherthan as shown in FIG. 6 are also possible. FIG. 15 and FIG. 16 showexamples of these. Only oscillation detection electrodes T1 and T2 shownin FIG. 6 are provided in the example shown in FIG. 15. In the exampleshown in FIG. 16, only oscillation detection electrodes T1 and T4 shownin FIG. 6 are provided.

FIG. 17 is a block diagram showing the configuration of the drivecircuit 200 supplying drive voltage signal SDR to the drive electrodes33 of the diaphragm 10 in the present embodiment. This drive circuit 200has a function for controlling the frequency of drive voltage signal SDRto maintain substantially the greatest phase difference betweenlongitudinal oscillation and sinusoidal oscillation produced in thediaphragm 10. This method of frequency control is used in order toefficiently transfer the kinetic energy of diaphragm 10 to the rotor100. This is described in detail below.

FIG. 18 shows an example of the path described by contact 36 ofdiaphragm 10. Describing the x axis and z axis in the figure, the z axisis the axis for the longitudinal direction of diaphragm 10 as shown inFIG. 10, and the x axis is the axis perpendicular to the z axis in theplane containing the surfaces of the diaphragm 10. In FIG. 18 Ra is thepath of contact 36 when the frequency of drive voltage signal SDRmatches the resonance frequency fr of longitudinal oscillation, and Rdis the path of contact 36 when the frequency of drive voltage signal SDRmatches the resonance frequency fr2 of sinusoidal oscillation. Inaddition, Rb and Rc denote the path of contact 36 when the frequency ofthe drive voltage signal SDR is a frequency fb, fc (fb<fc) between frand fr2.

Because sinusoidal oscillations produced in diaphragm 10 are induced bythe longitudinal oscillation, the phase of sinusoidal oscillation isdelayed relative to the phase of longitudinal oscillation. The path ofcontact 36 is an elliptical path with a bulge as shown in FIG. 18instead of a linear path because there is a phase difference between thelongitudinal oscillation and sinusoidal oscillation. This phasedifference of the longitudinal oscillation and sinusoidal oscillationdepends on the frequency of the drive voltage signal SDR. When the phasedifference changes according to frequency, the shape of the ellipticalpath described by the contact 36 changes, and a change is also thoughtto occur in the rotational drive force applied to the rotor 100.

As also shown in FIG. 18, the orientation of the long diameter of theelliptical path gradually moves away from the z axis and slopes to anorientation parallel to the x axis as the frequency of the drive voltagesignal moves from the resonance frequency fr of longitudinal oscillationto the resonance frequency fr2 of sinusoidal oscillation. When the slopeof the elliptical path of contact 36 thus changes due to change in thefrequency of the drive voltage signal SDR, the magnitude of therotational drive force applied to the rotor 100 is also thought tochange.

Following the above lines of thought, the inventors investigated therelationship between the frequency of the drive voltage signal SDR androtation of the rotor 100 in detail. FIG. 19 shows the frequencycharacteristic of diaphragm 10 obtained as a result of theseinvestigations: the horizontal axis denotes the frequency of the drivesignal applied to the drive electrodes of the diaphragm 10, the firstvertical axis on the left denotes the phase difference, and the secondvertical axis on the right denotes the rotational speed of the rotor 100driven by contact 36. Graph θ1 denotes the phase difference between thephase of the drive voltage signal SDR applied to drive electrodes 33 andthe phase of detection signal SD1 obtained from oscillation detectionelectrodes T1. Graph θ2 denotes the phase difference between the phaseof the drive voltage signal SDR applied to drive elect codes 33 and thephase of detection signal SD2 obtained from oscillation detectionelectrodes T2. Graph θ denotes φ2−θ1, that is, the phase differencebetween the phase of detection signal SD1 obtained from oscillationdetection electrodes T1 and the phase of detection signal SD2 obtainedfrom oscillation detection electrodes T2. This phase difference isequivalent to the phase difference between the phase of longitudinaloscillation and the phase of sinusoidal oscillation. Graph V denotes therotational speed of the rotor 100.

As will be known from FIG. 19, when the frequency of the drive voltagesignal SDR applied to diaphragm 10 is near 287 kHz, the phase differenceof detection signal SD1 and detection signal SD2, that is, phasedifference φ of longitudinal oscillation and sinusoidal oscillation, isgreatest, and the rotational speed V of rotor 100 is also highest atthis time.

The drive circuit 200 shown in FIG. 17 was designed with considerationfor the characteristics of such a diaphragm 10, and controls thefrequency of drive voltage signal SDR in order to maintain thesubstantially greatest phase difference between detection signals SD1and SD2.

This drive circuit 200 has a driver 201, φ-V conversion circuit 202,delay circuit 203, comparator circuit 204, voltage adjusting circuit205, and VCO (voltage-controlled oscillator) 206.

The driver 201 is a circuit for amplifying output signal Sdr of VCO 206and applying drive voltage signal SDR to drive electrodes 33 ofdiaphragm 10. It should be noted that in the initialized state thedriver 201 outputs a drive voltage signal SDR of a specific defaultfrequency. Output of this drive voltage signal SDR at the defaultfrequency is to set the initial oscillations of the diaphragm 10, thatis, to make the diaphragm 10 oscillate at the default frequency in theinitialization state. This initialization can be achieved by suchmethods as inputting a signal with a default frequency to the driver201, or applying a frequency control voltage for oscillating at thedefault frequency to the VCO 206.

When the diaphragm 10 oscillates due to application of the drive voltagesignal SDR, detection signal SD1 and detection signal SD2 are outputfrom oscillation detection electrodes T1 and T2 of diaphragm 10. The φ-Vconversion circuit 202 is a circuit for outputting a signal according tothe phase difference of detection signal SD1 and detection signal SD2,and as shown in FIG. 20 has a phase difference detector 202A and anaverage voltage converter 202B. FIG. 21 and FIG. 22 show the waveformsat parts of the φ-V conversion circuit 202. The phase differencedetector 202A generates a phase difference signal SDD of a pulse widthequivalent to the phase difference of detection signals SD1 and SD2. Theaverage voltage converter 202B averages the phase difference signalsSDD, and outputs a phase difference signal SPD at a level proportionalto the phase difference of detection signals SD1 and SD2. In the exampleshown in FIG. 21 the phase difference of detection signals SD1 and SD2is small. As a result, a phase difference signal SDD with a small pulsewidth θ1 is output, and a phase difference signal SPD with a low voltagelevel Vav1 is output. In the example shown in FIG. 22, the phasedifference of detection signals SD1 and SD2 is large. As a result, aphase difference signal SDD with a large pulse width θ2 is output, and aphase difference signal SPD with a high voltage level Vav2 is output.

Phase difference signal SPD is supplied to comparator circuit 201. SPDis also delayed a specific time by the delay circuit 203, and thensupplied to the comparator circuit 204 as signal DSPD.

The comparator circuit 204 determines the difference of signal SPD andsignal DSPD, determines if the time derivative of the phase differenceof signals SD1 and SD2 is positive or negative, and based on the resultof this determination applies voltage adjustment control signal SCT tovoltage adjusting circuit 205.

The voltage adjusting circuit 205 increases or decreases the frequencycontrol voltage SVC applied to VCO 206 according to the voltageadjustment control signal SCT applied from comparator circuit 204. TheVCO 206 oscillates at a frequency determined by this frequency controlvoltage SVC, and outputs signal Sdr to the driver 201.

In the drive circuit 200 thus described, control increasing theoscillation frequency of the VCO 206 is applied by the comparatorcircuit 204 when the phase difference of detection signals SD1 and SD2increases due to an increase of the oscillation frequency of VCO 206. Inaddition, when the phase difference of detection signals SD1 and SD2decreases due to an increase in the oscillation frequency of VCO 206,control lowering the oscillation frequency of VCO 206 is applied by thecomparator circuit 204. As a result of applying such control, VCO 206oscillates at a frequency maintaining the substantially greatest phasedifference between detection signals SD1 and SD2.

[1.4] Operation of this Embodiment

FIG. 23 is a flow chart showing the operation of the drive circuit 200in the present embodiment. Operation of the present embodiment isdescribed below according to this flow chart. When a time at which thedate changes and date counter 50 must be turned the amount for one daycomes, a start operation command is applied to the drive circuit 200from a control circuit not shown in the figures, and the initializationdrive signal is applied to the driver 201 for a specific period of time.While this initialization drive signal is applied to the driver 201, thefrequency of the initialization drive signal gradually rises with time.The range of change in the frequency of the initialization drive signalis set to a frequency range sufficiently lower than the frequency atwhich the phase difference of longitudinal oscillation and sinusoidaloscillation in the diaphragm 10 is maximized. The driver 201 amplifiesthe default drive signal thus supplied to apply it as drive voltagesignal SDR to the diaphragm 10. As a result, the diaphragm 10 beings tooscillate, and the frequency gradually rises.

When the specified time passes, supplying the default drive signal stopsand drive circuit 200 operates according to the flow shown in FIG. 21.First, when detection signals SD1 and SD2 are output from oscillationdetection electrodes T1 and T2 due to oscillation of the diaphragm 10,they are input to Φ-V conversion circuit 202 (step S1). The Φ-Vconversion circuit 202 detects the phase difference Φ of detectionsignals SD1 and SD2, and outputs average phase difference voltage signalSPD having a voltage VΦ equivalent to the average phase difference (stepS2). The delay circuit 203 receives this average phase differencevoltage signal SPD from the Φ-V conversion circuit 202 (step S3): then,time tp after receiving SPD from the conversion circuit 202, the delaycircuit 203 outputs the average phase difference voltage signal SPD assignal DSPD (step S4). When comparator circuit 204 receives signal SPDand signal DSPD (step S5), it determines if voltage VΦ of signal SPD isgreater than VΦtp of signal DSPI).

It is assumed here, for example, that the phase difference φ ofdetection signals SD1 and SD2 is φk shown in FIG. 19, and a signal SPDwith voltage Vφ corresponding to this φk is applied to the comparatorcircuit 204. Furthermore, at the time earlier by time tp the phasedifference φ of detection signals SD1 and SD2 is φj, which is less thanφk, and a signal DSPD of voltage Vφtp corresponding thereto is appliedto the comparator circuit 204. The result of step S6 in this case is YESbecause Vφ>Vφtp. In this case the comparator circuit 204 sends a highlevel voltage adjustment control signal SCT to the voltage adjustingcircuit 205 (step S7), and voltage adjusting circuit 205 increases thefrequency control voltage SVC applied to the VCO 206 (steps S8, S11).When frequency control voltage SVC thus rises, the oscillation frequencyof VCO 206 rises (steps S12, S13).

The same operation described above repeats for as long as phasedifference φ increases due to an increase in the frequency of drivevoltage signal SDR. As a result, drive voltage signal SDR graduallyincreases, and the phase difference φ of detection signals SD1 and SD2gradually rises accordingly (see arrow P in FIG. 19).

As shown by way of example in FIG. 19, phase difference φ is greatest ata particular frequency (a frequency near 287 kHz in FIG. 19), but thereare cases with the above operation in which the drive voltage signal SDRexceeds this frequency. The following operation is applied in suchcases.

First, if the phase difference φ of detection signals SD1 and SD2 at aparticular time is φn shown in FIG. 19, for example, a signal SPD of avoltage Vφ corresponding to φn is applied to the comparator circuit 204.At the time earlier by time tp the phase difference φ of detectionsignals SD1 and SD2 is φm, which is greater than φn, and signal DSPD ofvoltage Vφtp corresponding thereto is applied to the comparator circuit204. The result returned by step S6 in this case is NO because Vφ<Vφtp.In this case the comparator circuit 204 sends a low level voltageadjustment control signal SCT to the voltage adjusting circuit 205 (stepS9), and the voltage adjusting circuit 205 lowers the frequency controlvoltage SVC applied to VCO 206 (steps S10, S11). When the frequencycontrol voltage SVC thus drops, the oscillation frequency of VCO 206drops (steps S12, S13). As a result, phase difference φ, which haddropped, rises again as indicated by arrow Q in FIG. 19.

As a result of repeating such control the frequency of drive voltagesignal SDR is held to a frequency at which the phase difference φ ofdetection signals SD1 and SD2, that is, the phase difference oflongitudinal oscillation and sinusoidal oscillation of diaphragm 10, issubstantially maximized, and rotor 100 rotates at the highest rotationalspeed. Rotational drive of the rotor 100 is also transferred by thecalendar display mechanism shown in FIG. 1 and the date counter 50 turnsonly an angle equivalent to one day. The control circuit sends a drivestop command to the drive circuit 200 when it detects from a change inthe voltage of contact 65 that the date counter 50 has turned an angleequivalent to one day. As a result, the drive circuit 200 stopsoutputting drive voltage signal SDR.

[2] Embodiment 2

This embodiment and the first embodiment described above differ only inthe configuration of the drive circuit, and the other parts aretherefore described with reference to the same figures as the firstembodiment.

FIG. 24 is a block diagram showing the configuration of the drivecircuit 200A according to the present embodiment of the invention. Thisdrive circuit 200A does not have a delay circuit 203 such as used in thedrive circuit 200 of the first embodiment. The drive circuit 200Ainstead has a voltage regulator circuit 210. This voltage regulatorcircuit 210 outputs reference voltage SREF to comparator circuit 204A.This reference voltage SREF is a voltage of the same level as thevoltage output from φ-V conversion circuit 202 when the phase differenceφ of detection signals SD1 and SD2 obtained from diaphragm 10 isreference phase difference φd. This reference phase difference φd is aphase difference slightly lower than the maximum phase difference φ ofdetection signals SD1 and SD2 from diaphragm 10. When voltage SPD outputfrom φ-V conversion circuit 202 is lower than reference voltage SREF,the comparator circuit 204A outputs a voltage adjustment command signalinstructing an increase in frequency control voltage SVC causing theoscillation frequency of VCO 206 to rise. When voltage SPD is lower thanreference voltage SREF, comparator circuit 204A outputs a voltageadjustment command signal instructing a decrease in frequency controlvoltage SVC, and the oscillation frequency of the VCO 206 decreases.

FIG. 25 is a flow chart showing the operation of drive circuit 200A inthe present embodiment. Operation of the present embodiment is describedbelow according to this flow chart. When detection signals SD1 and SD2from diaphragm 10 are input to φ-V conversion circuit 202 (step S21),φ-V conversion circuit 202 detects phase difference φ of these detectionsignals SD1 and SD2, and outputs average phase difference voltage signalSPD having a voltage Vφ equivalent to this average phase difference(step S22). On the other hand, constant voltage circuit 210 constantlyoutputs reference voltage Vφd (step S23). When the comparator circuit204 receives average phase difference voltage signal SPD and referencevoltage Vφd (step S24), it determines if voltage Vφ of signal SPD islower than reference voltage Vφd (step S25).

When diaphragm 10 first starts to oscillate, the frequency of drivevoltage signal SDR and the phase difference of detection signals SD1 andSD2 is small. As a result, step S25 returns YES. In this case comparatorcircuit 204 outputs a high level voltage adjustment control signal SCTto voltage adjusting circuit 205 (step S26) and voltage adjustingcircuit 205 increases the frequency control voltage SVC applied to theVCO 206 (steps S27, S30). When the frequency control voltage SVC thusrises, the oscillation frequency of VCO 206 rises (steps S31, S32).

The operation described above repeats when the phase difference φ ofdetection signals SD1 and SD2 is less than reference phase difference φdand voltage Vφ of signal SPD is less than reference voltage Vφd. As aresult, the oscillation frequency of VCO 206 gradually rises, and thephase difference φ of detection signals SD1 and SD2 increases. Whenphase difference φ exceeds reference phase difference φd and voltage Vφof signal SPD exceeds reference voltage Vφd, step S25 returns NO.

In this case comparator circuit 204 sends a low level voltage adjustmentcontrol signal SCT to voltage adjusting circuit 205 (step S28), andvoltage adjusting circuit 205 reduces the frequency control voltage SVCapplied to VCO 206 (steps S29, S30). As a result, the oscillationfrequency of VCO 206 drops when frequency control voltage SVC drops(step S31, S33).

As a result of repeating this control, the frequency of drive voltagesignal SDR is held at a frequency at which the phase difference φ ofdetection signals SD1 and SD2, that is, the phase difference oflongitudinal oscillation and sinusoidal oscillation of diaphragm 10,goes to the reference phase difference φd, and rotor 100 rotates at anappropriate rotational speed. Rotational drive of the rotor 100 is alsotransferred by the calendar display mechanism shown in FIG. 1 and thedate counter 50 turns only an angle equivalent to one day. The controlcircuit sends a drive stop command to the drive circuit 200 when itdetects from a change in the voltage of contact 65 that the date counter50 has turned an angle equivalent to one day. As a result, the drivecircuit 200 stops outputting drive voltage signal SDR.

[3] Embodiment 3

In the second embodiment described above the frequency of drive voltagesignal SDR is controlled so that the phase difference of detectionsignals SD1 and SD2 obtained from diaphragm 10 goes to reference phasedifference φd. In order to efficiently drive the rotor 100 with suchfrequency control, reference phase difference φd must be set as high aspossible within a range not exceeding the maximum phase difference ofdetection signals SD1 and SD2 obtained from diaphragm 10. However, themaximum phase difference of detection signals SD1 and SD2 differs withindividual piezoactuators and even with load and temperature. FIG. 26shows the frequency characteristic of drive efficiency and the phasedifference of detection signals SD1 and SD2 at a temperature of 25° C.,and FIG. 27 shows the same frequency characteristic at a temperature of60° C. If the reference phase difference φd is set to 60°, the frequencyof drive voltage signal SDR achieving this phase difference when thetemperature is 60° C. can be determined. However, the frequency of thedrive voltage signal SDR at which the phase difference of detectionsignals SD1 and SD2 goes to reference phase difference φd cannot bedetermined when the temperature is 25° C.

This third embodiment of the invention solves this problem. FIG. 28 is ablock diagram showing the configuration of a drive circuit 200B in thepresent embodiment. This drive circuit 200B comprises a frequencycounter 211, control unit 212, and non-volatile memory 213 such as RAMbacked up by battery added to the configuration of the drive circuit200A in the second embodiment (FIG. 24).

The frequency counter 211 is a circuit for measuring the frequency ofthe drive voltage signal SDR. The non-volatile memory 213 has the job ofstoring the reference phase difference φd. When a piezoactuatoraccording to the present embodiment is used in a wristwatch, asufficiently large reference phase difference is stored to non-volatilememory 213. For example, the maximum possible phase difference ofdetection signals SD1 and SD2 or a greater value is first stored to thenon-volatile memory 213. The reference phase difference in thisnon-volatile memory 213 is then updated by control unit 212 each timerotor 100 is driven. The control unit 212 determines the reference phasedifference φd when rotor 100 is driven, and instructs the constantvoltage circuit 210 to output reference voltage SREF corresponding tothis reference phase difference φd. The reference phase differencestored to non-volatile memory 213 is referenced to determine referencephase difference φd. The control unit 212 also controls optimizing thereference phase difference in non-volatile memory 213.

Operation of drive circuit 200B when rotor 100 is driven three times isshown in FIG. 29.

When the rotor 100 is driven the first time, φd7 is stored as thereference phase difference in non-volatile memory 213. The control unit212 therefore defines φd8, which is a specific amount greater than φd7,as reference phase difference φd, and commands the constant voltagecircuit 210 to output a corresponding reference voltage SREF. When areference voltage SREF corresponding to phase difference φd8 is outputby constant voltage circuit 210, the frequency of drive voltage signalSDR begins to rise. At first the phase difference φ of detection signalsSD1 and SD2 also rises in conjunction with the increase in the frequencyof drive voltage signal SDR. However, after this phase differencereaches a maximum level, the phase difference φ of detection signals SD1and SD2 decreases in conjunction with increase in the frequency of drivevoltage signal SDR. The frequency of drive voltage signal SDR thenreaches an upper frequency limit without phase difference φ reachingreference phase difference φd8.

The control unit 212 detects that the frequency of drive voltage signalSDR reached the maximum frequency from the measurement results fromfrequency counter 211. The control unit 212 at this time assumes thatdriving rotor 100 failed, and tells the constant voltage circuit 210 tostop reference voltage SREF. Next, control unit 212 decreases referencephase difference φd8 a specific amount to φd7, and tells the constantvoltage circuit 210 to output a corresponding reference voltage SREF andoperate the drive circuit 200B. In the example shown in the figure thisdrive attempt also ends in failure. Driving rotor 100 by drive circuit200B with the reference phase difference set to φd6 is also attempted,but this attempt also ends in failure. When the control unit 212 thenreduces the reference phase difference a specified amount from φd6 toφd5 and operates the drive circuit 200B, and the frequency of drivevoltage signal SDR reaches frequency f1, the rotor 100 is driven withoptimum efficiency. When the control unit 212 detects that driving rotor100 ended normally, it stores reference phase difference φd5 tonon-volatile memory 213.

Operation when driving the rotor a second time after this is describednext.

In this case control unit 212 attempts to drive the rotor 100 by meansof drive circuit 200B using φd6, which is a specific amount greater thanφd5 stored in non-volatile memory 213, as reference phase difference φd,but this ends in failure. The control unit 212 therefore lowers thereference phase difference from φd6 to φd5, and operates the drivecircuit 200B. This φd5 is the reference phase difference at which rotordrive was successful the first time. When the rotor is driven the secondtime, however, phase difference φd of detection signals SD1 and SD2obtained from diaphragm 10 is lower overall, and driving rotor 100 usingreference phase difference φd5 also fails. As a result, the control unit212 operates the drive circuit 200B using φd4, which is a specificamount less than φd5, as the reference phase difference. In this casephase difference φ of detection signals SD1 and SD2 goes to referencephase difference φd4 when the frequency of drive voltage signal SDRreaches frequency f2. As a result, the rotor 100 is driven with optimumefficiency. When the control unit 212 detects that driving rotor 100ended normally, it stores reference phase difference φd4 to non-volatilememory 213.

Operation when driving the rotor a third time after this is describednext.

In this case control unit 212 attempts to drive the rotor 100 by meansof drive circuit 200B using φd5, which is a specific amount greater thanφd4 stored in non-volatile memory 213, as reference phase difference φd.Rotor drive failed the last time the reference phase difference was φd5.In this third rotor drive attempt, however, the phase difference φd ofdetection signals SD1 and SD2 obtained from diaphragm 10 is higheroverall, and driving rotor 100 using reference phase difference φd5 issuccessful. When the control unit 212 detects that driving rotor 100ended normally, it stores reference phase difference φd5 to non-volatilememory 213.

It will be noted that driving rotor 100 will be successful even if thereference phase difference φd is set to φd6, which is a specific amountgreater. However, the rotor 100 is not driven using this reference phasedifference φd6 during the third rotor drive operation. This is becausethe date counter already turned using reference phase difference φd5 andthe drive object has been achieved. If there is no change in thecharacteristics of the diaphragm 10 the fourth time the rotor is driven,the rotor will be driven using reference phase difference φd6 at thattime and reference phase difference φd6 will likely be stored tonon-volatile memory 213.

As described above the present embodiment tracks changes in thecharacteristics of the piezoactuator, and is able to drive the rotor 100with extremely high efficiency.

[4] Embodiment 4

FIG. 30 is a block diagram showing the configuration of a drive circuit200C for a piezoactuator in a fourth embodiment of this invention. InFIG. 30 VCO 206, driver 201, and φ-V conversion circuit 202 are the sameas in the drive circuit 200 (FIG. 17) in the first embodiment, anddescription thereof is omitted.

A/D converter 214 is a circuit for converting the phase differencesignal SPD output from φ-V conversion circuit 202 to a digital valueaccording to a command from control unit 212A. Operating unit 215 is acircuit for determining the digital value DF of the frequency controlvoltage SVC supplied to VCO 206 according to a command from control unit212A. Non-volatile memory 213A is memory for storing the digital valueDF for frequency control and the digital value of the phase differencesignal SPD when driving the rotor 100. The control unit 212A is a devicefor controlling each of the above-described parts. This control unit212A has a function for calculating by means of the operating unit 215an optimized digital value DF for frequency control considered toimprove piezoactuator drive efficiency over the present when drivecircuit 200C is driven to drive rotor 100, and update digital value DF.

FIG. 31 is a flow chart of this digital value DF update operation.Control unit 212A performs this routine for rotor drive. First, controlunit 212A sends the digital value DF stored to non-volatile memory 213Adirectly to D/A converter 216 through operating unit 215, causing it tooutput a corresponding frequency control voltage SVC (step S31). Whenthis frequency control voltage SVC is output from D/A converter 216, VCO206 oscillates at a corresponding frequency, and a drive voltage signalSDR with the same frequency is applied to diaphragm 10. The diaphragm 10thus oscillates and motor 100 is driven. During this time the phasedifference φ of detection signals SD1 and SD2 obtained from diaphragm 10is detected by φ-V conversion circuit 202, and phase difference signalSPD is output.

Using this time while the rotor is driven, control unit 212A advances aprocess for updating DF and SPD in preparation for the next drive.First, the control unit 212A commands the A/D converter 214 to A/Dconvert this phase difference signal SPD (step S32).

Next, control unit 212A updates digital value DF in the non-volatilememory 213 according to the following process. First, it subtracts thedigital value (here assumed to be SPDO) in non-volatile memory 213 fromthe digital value (here assumed to be SPDN) of the phase differencesignal SPD obtained this time to determine difference P. Next, itobtains a new digital value DFN from the following equation usingoperating unit 215, and stores this as the new DF in non-volatile memory213 (step S33).DFN=DFO+α×ΔPwhere α is a constant optimized through tests and simulations.

Next, control unit 212A stores the digital value of phase differencesignal SPD obtained this time to non-volatile memory 213 (step S34).

The above operation is performed each time the piezoactuator is drivento optimize the drive frequency of diaphragm 10.

FIG. 32 and FIG. 33 show exemplary operations for optimizing the digitalvalue DF of each frequency control voltage.

First, in the example shown in FIG. 32, phase difference signal SPDobtained from diaphragm 10 during piezoactuator drive is |ΔP| greaterthan the previous time, the drive time. If this situation continuesthere is a chance that phase difference φ will increase by furtherincreasing the frequency of drive voltage signal SDR. Therefore, inpreparation for the next drive the digital value DF of the frequencycontrol voltage is increased just |α×ΔP|.

On the other hand, in the example shown in FIG. 33, phase differencesignal SPD obtained from diaphragm 10 during piezoactuator drive is |ΔP|lower than the previous time, the drive time. If the frequency of thedrive voltage signal SDR is left as is in this case, there is the chancethat phase difference φ will drop suddenly. Therefore, in preparationfor the next drive the digital value DF of the frequency control voltageis reduced just |α×ΔP|.

This embodiment also achieves the effect of tracking change inpiezoactuator characteristics to drive the rotor 100 with extremely highefficiency.

[5] Other Applications for a Piezoactuator According to the PresentInvention

The calendar display mechanism of a wristwatch described above is notthe only application for a piezoactuator according to the presentinvention. This piezoactuator can also be applied in a variety of otherapplications. Examples of these are described below.

[5.1] Other Applications (1)

FIG. 34 is an oblique view showing the appearance of a contactless typeIC card. A remaining balance display counter 401 for displaying theremaining balance is provided on the front side of the contactless typeIC card 400. The remaining balance display counter 401 displays afour-digit remaining balance, and as shown in FIG. 35 has a display part402 for displaying the two high digits and a display part 403 fordisplaying the two low digits.

FIG. 36 is a side view showing the configuration of the high digitdisplay part. 402. The high digit display part 402 is linked topiezoactuator A1 through intervening rotor 100A, and is driven by thedrive force of the rotor 100A. The main parts of the high digit displaypart 402 include drive gear 402A having a driving part 402A and rotatingone revolution when rotor 100A turns 1/n revolution, a first high digitdisplay wheel 402B that turns one graduation for each revolution of thedrive gear 402A, a second high digit display wheel 402C that rotates onegraduation for each revolution of the first high digit display wheel402B, and a holding pawl 402D for stopping the first high digit displaywheel 402B when the first high digit display wheel 402B does not turn.It should be noted that a holding pawl not shown in the figures forstopping the second high digit display wheel 402C is also provided forthe second high digit display wheel 402C.

The drive gear 402A rotates one revolution when the rotor 100A turns 1/nrevolution. The driving pawl 402A meshes with the feed gear part 402B3of the first high digit display wheel 402B, and the first high digitdisplay wheel 402B turns one graduation.

It should be noted that turning rotor 100A 1/n revolution is only oneoperating example and the invention shall not be so limited.Furthermore, turning the first high digit display wheel 402B onegraduation when the drive gear 402A turns one revolution is also justone example of operation, and the invention shall not be so limited.

In addition, when the first high digit display wheel 402B turns androtates one revolution, feed pin 402B disposed on the first high digitdisplay wheel 402B causes feed gear 402B2 to turn, turning feed gear402C of second high digit display wheel 402C meshed with feed gear 402B,and thereby turning the second high digit display wheel 402C onegraduation.

The low digit display part 403 is linked to piezoactuator A2 throughintervening rotor 100B and is driven by the drive power of the rotor10B. The main parts of the low digit display part 403 include drive gear403A having a driving pawl 403A1 and rotating one revolution when rotor100B turns 1/n revolution, a first low digit display wheel 403B thatturns one graduation for each revolution of the drive gear 403A, and asecond low digit display wheel 403C that rotates one graduation for eachrevolution of the first low digit display wheel 403B.

A front view of the low digit display part 403 is shown in FIG. 37 and aside view in FIG. 38.

The first low digit display wheel 403B has a feed gear part 403B1 meshedwith driving pawl 403A1 of drive gear 403A, and turns one graduation foreach one revolution of the drive gear 403A.

A feed pin 403B2 is also provided on the first low digit display wheel403B to turn feed gear 403B3 each time the first low digit display wheel403B turns one revolution, and thereby turn second low digit displaywheel 403C one graduation.

A holding pawl 403D of the first low digit display wheel 403B engagesthe feed gear part 403B1 when not turning to stop the first low digitdisplay wheel 403B. Holding pawl 403E of the second low digit displaywheel 403C engages feed gear part 403F when the second low digit displaywheel 403C is not turning to stop the second low digit display wheel403C.

In this configuration actuator A1 and actuator A2 are set to besynchronously driven by drive circuit 200B, and drive circuit 200B isdriven when a drive control signal equivalent to the transaction amountis input by an IC card chip not shown in the figures.

A remaining balance display can thus be achieved even in a thincontactless IC card, and because the display can be presented even whennot driven without requiring a power source, the balance can bedisplayed with low power consumption and the balance to that point canbe displayed even when the power supply is depleted.

[5.2] Other Applications (2)

A piezoactuator and drive circuit therefor according to the presentinvention are also suited to applications such as rotating a driven partonly a specific angle according to some sort of trigger. In a precedingembodiment the present invention was applied to a calendar displaymechanism as an example of a display mechanism for time-relatedinformation. Essentially, in each of the above embodiments the drivecircuit drives a piezoactuator when the time at which the date should beadvanced is reached, and this piezoactuator drives the calendar displaymechanism of the wristwatch and turns the date counter an amountequivalent to one day. In addition, wristwatches also have a displaymechanism for information relating to time, and application of thepiezoactuator to such display mechanisms is also possible. A drivemechanism for a second hand for displaying seconds is one such example.The present invention can be applied to the second hand drive mechanismby configuring the second hand drive system so that it is linked to arotor rotationally driven by the piezoactuator in the above embodiments.When thus configured the piezoactuator is also driven by the drivecircuit each time passage of one second is indicated by the clockcircuit. Piezoactuator drive in this case lasts until piezoactuatordrive force is transferred through the rotor to the second hand drivemechanism and the second hand advances one second.

[6] Variations of the Embodiments

[6.1] First Variation

In order to converge the frequency of the drive voltage signal SDR tothe frequency at which the phase difference of the detection signals SD1and SD2 obtained from diaphragm 10 is greatest, the first embodimentdescribed above determines the time derivative of this phase difference,increases the frequency of the drive voltage signal SDR when the timederivative is positive, and decreases the frequency when negative. Inorder to quickly maximize the phase difference of detection signals SD1and SD2, it is effective here to increase the gain of the closed loop(see FIG. 17) consisting of diaphragm 10, φ-V conversion circuit 202,delay circuit 203, comparator circuit 204, voltage adjusting circuit205, VCO 206, and driver 201. However, if the gain of this closed loopis too high, the closed loop responds excessively to slight changes inthe phase difference, and a frequency at which the phase difference isan extreme high value that is not the maximum may be captured so thatsweeping the frequency of drive voltage signal SDR stops. To addressthis problem, this variation inserts a loop filter with an adjustablefilter coefficient to a suitable place in the closed loop. By adjustingthe filter coefficient of the loop filter, this variation can adjust theclosed loop gain so that the phase difference of detection signals SD1and SD2 can be quickly driven to the true maximum.

[6.2] Second Variation

When the initial frequency of the drive voltage signal SDR is low in theabove first embodiment, the time required to bring the frequency of thedrive voltage signal SDR to the frequency at which the phase differenceof detection signals SD1 and SD2 is maximized becomes longer. In thepresent variation, therefore, when the frequency of the drive voltagesignal SDR converges to the frequency at which the phase difference ofdetection signals SD1 and SD2 is maximized during rotor 100 drive, thefrequency control voltage SVC at that time is converted to a digitalvalue and stored in memory. Then, the next time the rotor 100 is driventhe digital value stored in memory is converted to an analog voltage,and a frequency control voltage SVC that is lower by a specific amountis applied to the VCO 206 to start drive voltage signal SDR frequencycontrol. When thus comprised the time required for the frequency of thedrive voltage signal SDR to reach the frequency at which the phasedifference of detection signals SD1 and SD2 is maximized can beshortened.

[6.3] Third Variation

Longitudinal oscillation and sinusoidal oscillation can be separatelydetected with a piezoactuator in each of the above embodiments becauseelectrodes for detecting longitudinal oscillation and electrodes fordetecting sinusoidal oscillation are separately provided. A variationusing this characteristic is shown in FIG. 39.

This drive circuit 200D shown in FIG. 39 adds a gain control circuit 251to the drive circuit (see FIG. 17) in the first embodiment.

In order to appropriately drive the rotor 100, the amplitude of bothlongitudinal oscillation and sinusoidal oscillation must be high enoughto overcome the surface roughness of the rotor 100.

Therefore, the gain control circuit 251 of the present variationincreases the gain of the driver 201 to raise the drive voltage signalSDR when the magnitude of either longitudinal oscillation detectionsignal SD1 or sinusoidal oscillation detection signal SD2 obtained fromdiaphragm 10 is less than or equal to a threshold value. Automatic gaincontrol using both detection signals SD1 and SD2 in this way is able tostabilize driving the rotor 100 by means of contact 36.

It should be noted that this variation can also be applied to the drivecircuits of the second to fourth embodiments, and not just in the firstembodiment.

[6.4] Fourth Variation

As does the first embodiment above, the variation shown in FIG. 40 alsouses the ability to separately detect longitudinal oscillation andsinusoidal oscillation. This drive circuit 200E shown in FIG. 40 adds afailure detection circuit 252 to the drive circuit (see FIG. 17) in thefirst embodiment.

The amplitude of detection signal SD1 or SD2 decreases when thediaphragm 10 fails due, for example, to a crack developing in thepiezoelectric elements of the diaphragm 10. When a phenomenon such asthis is confirmed by the failure detection circuit 252, a signalindicative thereof is sent to the wristwatch control unit to display afailure.

This variation has the effect of being able to quickly inform the userwhen it becomes necessary to repair the piezoactuator.

It should be noted that this variation can also be applied to the drivecircuits of the second to fourth embodiments, and not just in the firstembodiment.

[6.5] Fifth Variation

When the above-described third embodiment sets a reference phasedifference to operate the drive circuit and successfully drives thepiezoactuator, it increases the reference phase difference a specificamount the next time the drive circuit is driven and attempts to drivethe piezoactuator. Therefore, if there is no change over time in thecharacteristics of the piezoactuator, drive fails at the first drivecircuit operation and drive succeeds the second time the drive circuitoperates, and this sequence repeats each time the piezoactuator isdriven. Conditions such as this are not desirable when this embodimentis applied to an apparatus driving the piezoactuator at relatively shorttime intervals. The present variation improves on this.

In the present variation control unit 212 of drive circuit 200B storesthe reference phase difference at which drive succeeded to non-volatilememory 213 each time the piezoactuator is driven. When the piezoactuatoris to be driven, the control unit 212 reads a specific number of pastreference phase differences stored to non-volatile memory 213 anddetermines if the reference phase differences are the same. If thedetermination is YES, control unit 212 determines that the piezoactuatorcharacteristics are stable over time, and for a specific periodthereafter omits the process increasing the initial reference phasedifference from the reference phase difference used the previous drivetime. After this specific period passes, it resumes the processincreasing the initial reference phase difference from the phasedifference used the previous drive time.

[6.6] Sixth Variation

In the second to fourth embodiments the frequency of drive voltagesignal SDR is controlled in order to achieve the greatest possible phasedifference φ within the range in which the phase difference φ ofdetection signals SD1 and SD2 increases with an increase in thefrequency of the drive voltage signal SDR (range in which the slope ispositive). The embodiments of the invention shall not, however, be solimited. That is, it is also possible to control the frequency of drivevoltage signal SDR to achieve the greatest possible phase difference φwithin the range in which the phase difference φ of detection signalsSD1 and SD2 decreases with an increase in the frequency of the drivevoltage signal SDR (range in which the slope is negative).

[6.7] Seventh Variation

A variation in which a part of the drive circuit is controlled bysoftware in the first to third embodiments above is also conceivable.Examples of software control in this case are described below.

<Variation of Embodiment 1 (FIG. 17)>

In this variation components other than the φ-V conversion circuit 202,VCO 206, and driver 201 are replaced by a CPU and memory. The memory isused for data storage and program storage. An A/D converter is alsodisposed after the φ-V conversion circuit 202, and a D/A converter isdisposed before the VCO 206.

In this variation the CPU executes the following process according toroutines stored in memory when a piezoactuator drive command isasserted.

S31: The digital value applied to the D/A converter is increased for aspecific time to raise the oscillation frequency of VCO 206 to theinitial value.

S32: Phase difference φ is received from the A/D converter, and the timederivative thereof is obtained.

S33: The digital value applied to the D/A converter is increased if thetime derivative is positive, and decreased if negative.

S34: Processing ends if the change in phase difference φ is within aspecific tolerance range, and processing otherwise returns to step S32.

<Variation of Embodiment 2 (FIG. 24)>

In this variation components other than the φ-V conversion circuit 202,VCO 206, and driver 201 are replaced by a CPU and memory. The memory isused for data storage and program storage. An A/D converter is alsodisposed after the φ-V conversion circuit 202, and a D/A converter isdisposed before the VCO 206.

In this variation the CPU executes the following process according toroutines stored in memory when a piezoactuator drive command isasserted.

S41: A digital value corresponding to the initial value of frequencycontrol voltage SVC is applied to the D/A converter.

S42: Phase difference φ is received from the A/D converter, and thedigital value applied to the D/A converter is increased if the phasedifference is less than the reference phase difference, and is decreasedif greater than.

S43: The process ends if the phase difference φ is within a specifictolerance range of the reference phase difference, and the processotherwise returns to step S42.

<Variation of Embodiment 3 (FIG. 28)>

In this variation components other than the frequency counter 211, φ-Vconversion circuit 202, VCO 206, and driver 201 are replaced by a CPUand memory. The memory is used for data storage and program storage. Thereference phase difference is stored as data in memory. An A/D converteris also disposed after the φ-V conversion circuit 202, and a D/Aconverter is disposed before the VCO 206.

In this variation the CPU executes the following process according toroutines stored in memory when a piezoactuator drive command isasserted.

S51: The failure count is initialized to 0, and the reference phasedifference is read from memory and increased a specific amount.

S52: The digital value applied to the D/A converter is initialized.

S53: Whether phase difference φ exceeds the reference phase differenceis determined, and the process skips to step S56 if the result is YES.

S54: The digital value applied to the D/A converter is increased aspecific amount.

S55: Whether the frequency of the drive voltage signal SDR output fromfrequency counter 211 is less than or equal to a specific value isdetermined; if the result is YES, the digital value applied to the D/Aconverter is increased a specific amount (S55A), and the routine returnsto step S53; if the result is NO, the failure count is incremented 1,the reference phase difference is decreased a specific amount (S55B),and the routine returns to step S52.S56: If the failure count is 0, the reference phase difference isincreased a specific amount (step S56A) and the routine returns to stepS52, otherwise the reference phase difference is stored to memory (stepS56B) and the process ends.

The present invention can also be achieved by such modes as distributingthe routines described above via an electrical communication circuit tousers, or storing such routines to a computer-readable storage mediumdistributed to users. The users can write the desired routines thusobtained to the drive circuit memory.

[6.7] Seventh Variation

Wristwatches and contactless IC cards are described above as theportable devices, but it will be noted that the present invention can beapplied to any type of portable device insofar as it is a portableelectronic device requiring a drive system, and particularly arotational drive system.

[6.8] Eighth Variation

A longitudinal oscillation mode oscillating in the longitudinaldirection of the piezoactuator is used as the first oscillation mode,and a sinusoidal oscillation mode corresponding to the first oscillationmode is used as the second oscillation mode in the embodiments describedabove, but the invention shall not be so limited.

Specifically, a first longitudinal oscillation mode that is alongitudinal oscillation mode oscillating lengthwise to thepiezoactuator can be used as a first oscillation mode, and a secondlongitudinal oscillation mode oscillating in a direction orthogonal tothe first oscillation mode can be used as the second oscillation mode.

Furthermore, it is also possible to use the above-noted secondlongitudinal oscillation mode as the first oscillation mode, and use asinusoidal oscillation mode corresponding to the second longitudinaloscillation mode.

The locations of the oscillation detection electrodes in these cases canbe determined from tests.

[6.9] Ninth Variation

In addition to using a battery (primary cell or secondary cell) as thepower source of the actuator, configurations using a power supply withan internal generator mechanism having a solar cell, thermoelectricgenerator, mechanical generator, or storage device (capacitor orsecondary battery) can also be used.

1. A drive circuit for a piezoactuator, comprising: at least onepiezoelectric element having a first oscillation mode and a secondoscillation mode, the at least one piezoelectric element being adaptedto oscillate when an AC signal is applied to it, the second oscillationmode having a different oscillation direction than that of the firstoscillation mode; a driver for applying an AC drive voltage signal tothe at least one piezoelectric element; and a frequency control unit fordetecting a first electrical signal from the at least one piezoelectricelement indicative of oscillation in the first oscillation mode, fordetecting a second electrical signal from the at least one piezoelectricelement indicative of oscillation in the second oscillation mode, andfor controlling the frequency of the AC drive voltage signal to optimizethe phase difference between the first and second electrical signals fora particular operating condition of the at least one piezoelectricelement, such that the phase difference is substantially maximized, thefrequency control unit further comprising: a phase difference detectioncircuit for detecting the phase difference between the first and secondelectrical signals; a time differentiating circuit for determining atime differential of the phase difference detected by the phasedifference detection circuit; and a frequency adjusting circuit forincreasing the frequency of the AC drive voltage signal when the timedifferential is positive, and decreasing the frequency of the AC drivevoltage signal when the time differential is negative.
 2. A drivecircuit for a piezoactuator as described in claim 1, wherein thefrequency control unit comprises a circuit for controlling the frequencyof the AC drive voltage signal so that the phase difference between thefirst and second electrical signals is substantially maximized.
 3. Adrive circuit for a piezoactuator as described in claim 2, wherein thefrequency control unit comprises: a phase difference detection circuitfor detecting the phase difference between the first and secondelectrical signals; a time differentiating circuit for determining atime differential of the phase difference detected by the phasedifference detection circuit; and a frequency adjusting circuit forincreasing the frequency of the AC drive voltage signal when the timedifferential is positive, and decreasing the frequency of the AC drivevoltage signal when the time differential negative.
 4. A drive circuitfor a piezoactuator as described in claim 2 1, further comprising avoltage-controlled oscillator for supplying an output signal to thedriver, wherein the frequency control unit controls the frequency of theAC drive voltage signal by increasing or decreasing a control voltageapplied to the voltage-controlled oscillator.
 5. A drive circuit for apiezoactuator as described in claim 4, wherein the frequency controlunit comprises a memory for storing the voltage level of the controlvoltage when the frequency of the AC drive voltage signal is controlledto maximize the phase difference, wherein the frequency control unitdetermines an initial level of the control voltage based on the voltagelevel of the control voltage stored in memory when frequency control ofthe AC drive voltage signal is initiated and then increases or decreasesthe control voltage accordingly.
 6. A drive circuit for a piezoactuatoras described in claim 1 , comprising: at least one piezoelectric elementhaving a first oscillation mode and a second oscillation mode, the atleast one piezoelectric element being adapted to oscillate when an ACsignal is applied to it, the second oscillation mode having a differentoscillation direction than that of the first oscillation mode; a driverfor applying an AC drive voltage signal to the at least onepiezoelectric element; and a frequency control unit for detecting afirst electrical signal from the at least one piezoelectric elementindicative of oscillation in the first oscillation mode, for detecting asecond electrical signal from the at least one piezoelectric elementindicative of oscillation in the second oscillation mode, and forcontrolling the frequency of the AC drive voltage signal to optimize thephase difference between the first and second electrical signals for aparticular operating condition of the at least one piezoelectricelement, wherein the frequency control unit comprises a circuit forcontrolling the frequency of the AC drive voltage signal so that thephase difference substantially corresponds to a reference phasedifference, wherein the frequency control unit further comprises: adrive evaluator adapted to determine if drive of the piezoactuatorsatisfies a particular performance characteristic; and an initialreference phase difference adjustor adapted to reduce the referencephase difference so that the piezoactuator satisfies the particularperformance characteristic when the drive evaluator determines that thepiezoactuator does not satisfy the particular performancecharacteristic, and to increase the reference phase difference when thedrive evaluator determines that the piezoactuator satisfies theparticular performance characteristic.
 7. A drive circuit for apiezoactuator as described in claim 6, wherein the frequency controlunit comprises: a phase difference detection circuit for detecting thephase difference between the first and second electrical signals; acomparator for comparing the phase difference detected by the phasedifference detection circuit with the reference phase difference; and afrequency adjusting circuit for increasing or decreasing the frequencyof the AC drive voltage signal based on the comparison result obtainedby the comparator.
 8. A drive circuit for a piezoactuator as describedin claim 7, wherein the frequency control unit further comprisesvoltage-controlled oscillator for supplying an output signal to thedriver; and herein the frequency adjusting circuit comprises a voltageadjusting circuit for increasing or decreasing the control voltageapplied to the voltage-controlled oscillator based on the comparisonresult obtained by the comparator.
 9. A drive circuit for apiezoactuator as described in claim 6, wherein the frequency controlunit comprises: a drive evaluator adapted to determine if drive of thepiezoactuator satisfies a particular performance characteristic; and aninitial reference phase difference adjustor adapted to reduce thereference phase difference so that the piezoactuator satisfies theparticular performance characteristic when the drive evaluatordetermines that the piezoactuator does not satisfy the particularperformance characteristic, and to increase the reference phasedifference when the drive evaluator determines that the piezoactuatorsatisfies the particular performance characteristic.
 10. A drive circuitfor a piezoactuator as described in claim 9 6, wherein, when it isdetermined that the reference phase difference at which thepiezoactuator drive satisfies the particular performance characteristicis substantially the same for a predetermined consecutive number oftimes, the initial reference phase difference adjustor is controlled tonot increase nor decrease the reference phase difference for apre-specified period of time.
 11. A drive circuit for a piezoactuator asdescribed in claim 9 6, wherein the frequency control unit comprises afrequency counter for measuring the frequency of the AC drive voltagesignal, and wherein the drive evaluator determines whether or not thepiezoactuator satisfies the particular performance characteristic basedon whether or not the frequency measured by the frequency counter iswithin a predetermined range.
 12. A drive circuit for a piezoactuatorasdescribed in claim 6 , comprising: at least one piezoelectric elementhaving a first oscillation mode and a second oscillation mode, the atleast one piezoelectric element being adapted to oscillate when an ACsignal is applied to it, the second oscillation mode having a differentoscillation direction than that of the first oscillation mode; a driverfor applying an AC drive voltage signal to the at least onepiezoelectric element; and a frequency control unit for detecting afirst electrical signal from the at least one piezoelectric elementindicative of oscillation in the first oscillation mode, for detecting asecond electrical signal from the at least one piezoelectric elementindicative of oscillation in the second oscillation mode, and forcontrolling the frequency of the AC drive voltage signal to optimize thephase difference between the first and second electrical signals for aparticular operating condition of the at least one piezoelectricelement, wherein the frequency control unit comprises a circuit forcontrolling the frequency of the AC drive voltage signal so that thephase difference substantially corresponds to a reference phasedifference, wherein the frequency control unit further comprises: meansfor obtaining, each time the piezoactuator is driven, an indication of achange in the phase difference between the first and second electricalsignals from a previous drive operation of the piezoactuator; and meansfor increasing or decreasing the reference phase difference according tothe change in the phase difference.
 13. A method for controlling a drivecircuit having at least one oscillatible piezoelectric element of apiezoactuator, the method comprising the steps of: applying an AC drivevoltage signal to the at least one piezoelectric element; outputting anoutput signal having a frequency corresponding to a frequency of acontrol voltage; receiving a first electrical signal from the at leastone piezoelectric element indicative of oscillation in a firstoscillation mode and receiving a second electrical signal from the atleast one piezoelectric element in indicative of oscillation in a secondoscillation mode, the second oscillation mode having an oscillationdirection different from that of the first oscillation mode; detecting aphase different between the first and second electrical signals; andoptimizing the oscillation frequency of the output signal based on thedetected phase difference, comprising increasing the oscillationfrequency if a time differential of the detected phase difference isgreater than zero, and decreasing the oscillation frequency if the timedifferential is less than zero, the increasing or decreasing beingperformed until the time differential of the phase difference over apre-specified period of time is within a specified range.
 14. A methodas described in claim 13, wherein the optimizing of the oscillationfrequency comprises increasing the oscillation frequency if a timedifferential of the detected phase difference is greater than (d/dt)₁,where (d/dt)₁ is greater than zero, and decreasing the oscillationfrequency if the time differential is less than (d/dt)₂, where (d/dt)₂is less than zero, the increasing or decreasing being performed untilthe time differential of the phase difference over a pre-specifiedperiod of time is between (d/dt)₁ and (d/dt)².
 15. A method as describedin claim 13, wherein the optimizing of the oscillation frequencycomprises increasing the oscillation frequency until the detected phasedifference is greater than or equal to a reference phase difference. 16.A method as described in claim 15, further comprising a step of forcontrolling a drive circuit having at least one oscillatiblepiezoelectric element of a piezoactuator, the method comprising thesteps of: applying an AC drive voltage signal to the at least onepiezoelectric element; outputting an output signal having a frequencycorresponding to a frequency of a control voltage; receiving a firstelectrical signal from the at least one piezoelectric element indicativeof oscillation in a first oscillation mode and receiving a secondelectrical signal from the at least one piezoelectric element indicativeof oscillation in a second oscillation mode, the second oscillation modehaving an oscillation direction different from that of the firstoscillation mode; detecting a phase difference between the first andsecond electrical signals; optimizing the oscillation frequency of theoutput signal based on the detected phase difference, wherein theoptimizing of the oscillation frequency comprises increasing theoscillation frequency until the detected phase difference is greaterthan or equal to a reference phase difference; and determining ifdriving the piezoactuator satisfies a particular performancecharacteristic, and correcting the reference phase difference based onthe determination.
 17. A device-readable medium embodying a controlprogram for controlling a drive circuit having at least one oscillatiblepiezoelectric element of a piezoactuator, the control programcomprising: applying an AC drive voltage signal to the at least onepiezoelectric element; outputting an output signal of a frequencycorresponding to a frequency control voltage; receiving a firstelectrical signal from the at least one piezoelectric element indicativeof oscillation in a first oscillation mode and receiving a secondelectrical signal from the at least one piezoelectric element indicativeof oscillation in a second oscillation mode, the second oscillation modehaving an oscillation direction different from that of the firstoscillation mode; detecting a phase difference between the first andsecond electrical signals; and optimizing the oscillation frequency ofthe output signal based on the detected phase difference, comprisingincreasing the oscillation frequency if a time differential of thedetected phase difference is greater than zero, and decreasing theoscillation frequency if the time differential is less than zero, theincreasing or decreasing being performed until the time differential ofthe phase difference over a pre-specified period of time is within aspecified range.
 18. A device-readable medium as described in claim 17,wherein the medium comprises a physical storage device or anelectromagnetic signal on which the program of instructions is carried.19. A portable electronic device, comprising: a piezoactuator comprisingat least one piezoelectric element having a first oscillation mode and asecond oscillation mode, the at least one piezoelectric element beingadapted to oscillate when an AC signal is applied to it, the secondoscillation mode having a different oscillation direction than that ofthe first oscillation mode; and a drive circuit comprising: a driver forapplying an AC drive voltage signal to the at least one piezoelectricelement; and a frequency control unit for detecting a first electricalsignal from the at least one piezoelectric element indicative ofoscillation in the first oscillation mode, for detecting a secondelectrical signal from the at least one piezoelectric element indicativeof oscillation in the second oscillation mode, and for controlling thefrequency of the AC drive voltage signal to optimize the phasedifference between the first and second electrical signals for aparticular operating condition, such that the phase difference issubstantially maximized, the frequency control unit further comprising:a phase difference detection circuit for detecting the phase differencebetween the first and second electrical signals; a time differentiatingcircuit for determining a time differential of the phase differencedetected by the phase difference detection circuit; and a frequencyadjusting circuit for increasing the frequency of the AC drive voltagesignal when the time differential is positive, and decreasing thefrequency of the AC drive voltage signal when the time differentialnegative.
 20. A portable electronic device as described in claim 19,wherein the portable electronic device is a wristwatch comprising: arotor adapted to be rotationally driven by the piezoactuator; and adisplay mechanism linked to the rotor for displaying information relatedto time.
 21. A portable electronic device as described in claim 19,wherein the portable electronic device is a contactless IC card.
 22. Aportable electronic device, comprising the drive circuit for apiezoactuator as described in claim 6.